Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D223/00—Heterocyclic compounds containing seven-membered rings having one nitrogen atom as the only ring hetero atom
  • C07D223/14—Heterocyclic compounds containing seven-membered rings having one nitrogen atom as the only ring hetero atom condensed with carbocyclic rings or ring systems
  • C07D223/18—Dibenzazepines; Hydrogenated dibenzazepines
  • C07D223/22—Dibenz [b, f] azepines; Hydrogenated dibenz [b, f] azepines
  • C07D223/24—Dibenz [b, f] azepines; Hydrogenated dibenz [b, f] azepines with hydrocarbon radicals, substituted by nitrogen atoms, attached to the ring nitrogen atom
  • C07D223/28—Dibenz [b, f] azepines; Hydrogenated dibenz [b, f] azepines with hydrocarbon radicals, substituted by nitrogen atoms, attached to the ring nitrogen atom having a single bond between positions 10 and 11
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
  • A61K31/00—Medicinal preparations containing organic active ingredients
  • A61K31/33—Heterocyclic compounds
  • A61K31/395—Heterocyclic compounds having nitrogen as a ring hetero atom, e.g. guanethidine or rifamycins
  • A61K31/55—Heterocyclic compounds having nitrogen as a ring hetero atom, e.g. guanethidine or rifamycins having seven-membered rings, e.g. azelastine, pentylenetetrazole
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61P—SPECIFIC THERAPEUTIC ACTIVITY OF CHEMICAL COMPOUNDS OR MEDICINAL PREPARATIONS
  • A61P25/00—Drugs for disorders of the nervous system
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61P—SPECIFIC THERAPEUTIC ACTIVITY OF CHEMICAL COMPOUNDS OR MEDICINAL PREPARATIONS
  • A61P25/00—Drugs for disorders of the nervous system
  • A61P25/08—Antiepileptics; Anticonvulsants
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61P—SPECIFIC THERAPEUTIC ACTIVITY OF CHEMICAL COMPOUNDS OR MEDICINAL PREPARATIONS
  • A61P31/00—Antiinfectives, i.e. antibiotics, antiseptics, chemotherapeutics
  • A61P31/04—Antibacterial agents
  • A61P31/08—Antibacterial agents for leprosy
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D223/00—Heterocyclic compounds containing seven-membered rings having one nitrogen atom as the only ring hetero atom
  • C07D223/14—Heterocyclic compounds containing seven-membered rings having one nitrogen atom as the only ring hetero atom condensed with carbocyclic rings or ring systems
  • C07D223/18—Dibenzazepines; Hydrogenated dibenzazepines
  • C07D223/22—Dibenz [b, f] azepines; Hydrogenated dibenz [b, f] azepines
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D223/00—Heterocyclic compounds containing seven-membered rings having one nitrogen atom as the only ring hetero atom
  • C07D223/14—Heterocyclic compounds containing seven-membered rings having one nitrogen atom as the only ring hetero atom condensed with carbocyclic rings or ring systems
  • C07D223/18—Dibenzazepines; Hydrogenated dibenzazepines
  • C07D223/22—Dibenz [b, f] azepines; Hydrogenated dibenz [b, f] azepines
  • C07D223/24—Dibenz [b, f] azepines; Hydrogenated dibenz [b, f] azepines with hydrocarbon radicals, substituted by nitrogen atoms, attached to the ring nitrogen atom
  • C07D223/26—Dibenz [b, f] azepines; Hydrogenated dibenz [b, f] azepines with hydrocarbon radicals, substituted by nitrogen atoms, attached to the ring nitrogen atom having a double bond between positions 10 and 11

Definitions

• the present invention relates to a process for the asymmetric catalytic reduction of oxcarbazepine (10, 11 -dihydro-10-oxo-5H-dibenz/b,f/azepine-5-carboxamide).
• Carbamazepine (I) and oxcarbazepine (II) are established first-line drugs used in the treatment of epilepsy:
• oxcarbazepine (II) is rapidly metabolised to a pharmacologically active 4:1 mixture of the (S) and (R) enantiomers of 10,11-dihydro- 10-hydroxy-5H-dibenz/b,f/azepine-5-carboxamide (III):
• WO02/096881 discloses a two-step process for the preparation of racemic (III) from carbamazepine.
• WO 02/092572 discloses a process for preparing a racemic mixture of (III) from oxcarbazepine and further discloses a process for resolving the (S) and (R)- enantiomers of (III) from the racemic mixture.
• the enantiomers can be used as intermediates in the preparation of (S)-(-)-10-acetoxy-10,l l-dihydro-5H- dibenz/b,f/azepihe-5-carboxamide and (R)-(+)-10-acetoxy-10,l l-dihydro-5H- dibenz/b,f/azepine-5-carboxamide, two single-isomer drugs that may be used to treat epilepsy and other disorders of the central nervous system (Benes et al, US 5,753,646).
• WO 2004/031155 discloses a method for the enantioselective preparation of the (S) and (R)-enantiomers of (EI) by asymmetric reduction of oxcarbazepine.
• the asymmetric reduction is carried out in the presence of a ruthenium catalyst and a hydride source.
• a suitable catalyst may be formed from [RuCl 2 (p-cymene)] 2 and (S,S)-N-(4- toluenesulfonyl)-diphenylethylenediamine (hereinafter referred to as (S 5 S)-TsDPEN).
• S 5 S)-TsDPEN A mixture of formic acid and triethylamine (in a 5:2 molar ratio) is used as the hydride source.
• the disclosed process uses a very low substrate: catalyst ratio, i.e. a high amount of catalyst, (e.g. a ratio of 86:1 in example 1).
• a high amount of catalyst e.g. a ratio of 86:1 in example 1.
• the first major disadvantage of using such a high amount of catalyst is that the residual level of ruthenium metal, a most undesirable contaminant in the product, will be high and difficult to remove, and therefore the product will be unsuitable for use as an active pharmaceutical ingredient (API) or as a late-stage API intermediate. Regulatory guidance for residual metals derived from catalysts exists and the oral concentration limits for ruthenium residues are controlled particularly tightly.
• the second major disadvantage is that the ruthenium catalyst is expensive. The catalyst system described in WO 2004/031155 is very inefficient, and the cost contribution of the catalyst system alone prevents the process from being economically viable for large-scale manufacturing purposes.
• the process disclosed in WO 2004/031155 also uses large quantities of the hydride source (7 equivalents of formic acid and 2.7 equivalents of triethylamine).
• Commercial sources of the formic acid/triethylamine mixture (triethylammonium formate) are available, but the mixture is expensive.
• the considerable excess of formic acid used in the process is potentially hazardous as the formic acid can decompose in the presence of the catalyst, causing gradual or spontaneous liberation of carbon dioxide and flammable hydrogen gas as well as causing pressure build-ups inside the reactor vessel.
• Premature degradation of the hydride source also means that the reduction reaction is slowed down considerably and does not reach full conversion even on prolonged reaction times, making the reaction even less efficient and ultimately providing product of low purity.
• the present invention thus seeks to provide an improved method for the preparation of (S)-(+)-10,l l-dihydro-10-hydroxy-5H-dibenz/b,f/azepine-5-carboxamide and (R)-(-)-10,l l-dihydro-10-hydroxy-5H-dibenz/b,f/azepine-5-carboxamide, wherein the method is readily amenable to industrial batch-size production.
• the present invention provides a process for preparing (S)-(+)-
• R 1 is chosen from Ci -6 alkoxy and Cj -6 alkyl, n is a number from 0 to 5, and when n is a number from 2 to 5, R 1 can be the same or different, and R 2 is alkyl, substituted alkyl, aryl, substituted aryl, alkaryl or substituted alkaryl; wherein the hydride source is either NR 3 R 4 R 5 and formic acid, or [R 3 R 4 R 5 NH][OOCH] and optionally formic acid, or [M][OOCH] x and formic acid, wherein R 3 , R 4 and R 5 are Ci -6 alkyl, M is an alkali metal or alkaline earth metal and x is 1 or 2, and wherein during the process a pH from 6.5 to 8 is maintained.
• the present invention makes it possible to obtain optically pure (S)-(+)-10,l 1- dihydro-10-hydiOxy-5H-dibenz/b,f/azepine-5-carboxamide or (R)-(-)-10,l l-dihydro-10- hydroxy-5H-dibenz/b,f/azepine-5-carboxamide
• optically pure is used to include compounds which have optical purity from 75-100%, preferably from 92- 99.5%, more preferably from 96-99.5%.
• T'he active catalyst is prepared from [RuX 2 (L)J 2 , and a ligand of formula (A) or formula (B):
• X is chlorine, bromine or iodine, preferably chlorine
• L is an aiyl or aryl- aliphatic ligand such as p-cymene (isopropylmethylbenzene), benzene, hexamethylbenzene or mesitylene, and is preferably p-cymene
• R 1 is chosen from Cj -6 alkoxy and Ci -6 alkyl, and n is a number from 0 to 5. When n is a number from 2 to 5, R 1 can be the same or different.
• n is either 0 or 1 and when n is 1, R 1 is preferably either a methoxy or methyl group. Most preferably, R 1 is a methoxy group in the para position.
• R 2 is an alkyl, substituted alkyl, aryl, substituted aryl, alkaryl or substituted alkaryl group, wherein the alkyl may be straight-chain, branched, cyclic or bridged and the alkyl, aryl or alkaryl groups may be substituted with alkyl, alkoxy, halogen or keto groups.
• the R 2 group is an alkyl group, it may suitably contain 1 to 9 carbon atoms.
• the alkyl group substituent may suitably contain 1 to 9 carbon atoms.
• the alkoxy or keto group substituent may suitably contain 1 to 9 carbon atoms. It is preferred that the alkoxy group substituent is methoxy.
• R 2 groups are shown below:
• R 2 is preferably a phenyl group substituted by methyl, most preferably a phenyl group substituted by methyl at the para-position.
• Preferred ligands of formula (A) and (B) are shown below:
• the most preferred ligands are (S 5 S)-TsDAEN and (R 5 R)-TsDAEN. It has been surprisingly discovered that substitution of the phenyl rings in particular by a methoxy substituent gives rise to a catalyst having greater efficiency for the asymmetric reduction of oxcarbazepine. Accordingly, much lower quantities of this catalyst are required for the preparation of (S) and (R)-IO 5 I l-dihydro-10-hydroxy-5H-dibenz/b,f/azepine-5- carboxamide from oxcarbazepine when compared to other ligands.
• Processes using catalysts formed from ligands of formula (A) provide (S)-(+)- 10,l l-dihydro-10-hydroxy-5H-dibenz/b,f/azepine-5-carboxamide and processes using catalysts formed from ligands of formula (B) provide (R)-(-)-10,l l-dihydro-10-hydroxy- 5H-dibenz/b,f/azepine-5-carboxamide.
• the catalyst is preferably prepared in situ, e.g. by combining [RuX 2 L] 2 and the ligand of formula (A) or (B) under inert atmosphere in a solvent such as dimethylformamide (DMF).
• a solvent such as dimethylformamide (DMF).
• Figure 1 provides an example of the catalytic cycle that is believed to take place (the hydride source in this example is [Et 3 NH][OOCH]).
• the molar ratio of oxcarbazepine to the ruthenium catalyst (which is equivalent to the molar ratio of oxcarbazepine to ruthenium) is suitably at least 500:1, preferably at least 1000:1, more preferably at least 1500:1.
• the process can been operated successfully at a molar ratio of oxcarbazepine to the ruthenium catalyst of 2700:1, therefore it is envisaged that the process can be operated with advantage, at oxcarbazepine to ruthenium catalyst ratios of at least 2000:1, more preferably at least 2500:1. It is expected that the process can be operated with oxcarbazepine to ruthenium catalyst ratios of at least 3000:1.
• Molar ratios lower than 500:1 are not preferred because the precious metal catalyst is expensive and may result in unacceptably high residual ruthenium levels in the isolated product.
• the process of the invention wherein the pH of the reaction mixture is controlled allows for a significantly improved substrate: catalyst ratios compared to prior art methods wherein the pH is not controlled, e.g. example 1 process of WO 2004/03115 uses an oxcarbazepine to ruthenium ratio of 86:1.
• the hydride source is either NR 3 R 4 R 5 and formic acid, or [R 3 R 4 R 5 NH][OOCH] and optionally formic acid, or [M][OOCH] x and formic acid, wherein R 3 , R 4 and R 5 are C] -6 alkyl, M is an alkali metal or alkaline earth metal and x is 1 or 2.
• R 3 , R 4 and R 5 may be the same or different, but are preferably all the same.
• the Ci -6 alkyl groups may be straight-chain, branched or cyclic.
• R 3 , R 4 and R 5 are ethyl, propyl or butyl, most preferably ethyl.
• M is preferably Na, Li or K, most preferably Na. When M is an alkali metal x is 1 and when M is an alkaline earth metal, x is 2.
• [R 3 R 4 R 5 NH][OOCH] reagents e.g. [Et 3 NH][OOCH]
• [Et 3 NH][OOCH] is commonly used in asymmetric reduction reactions but is synthesised from H 2 , CO 2 and NEt 3 in the presence of a ruthenium catalyst and is therefore expensive, so it is desirable to minimise the use of this type of reagent.
• the hydride source is NR 3 R 4 R 5 and formic acid, preferably triethylamine and formic acid.
• the NR 3 R 4 R 5 is added to the reaction mixture at the start of the process.
• the amount of formic acid that is added to the reaction mixture at the start of the process can be minimised. This is advantageous because the formic acid decomposes to carbon monoxide and hydrogen during the process, and this is potentially hazardous if large quantities of formic acid are used.
• formic acid Suitably less than 1.5 equivalents of formic acid are added to the reaction mixture at the start of the process, preferably less than 1 equivalent, most preferably less than 0.2 equivalents. If less than 1 equivalent of formic acid is added at the start of the process, further formic acid should be added during the course of the reaction, providing about 1- 3 equivalents of formic acid in total.
• the hydride source is [R 3 R 4 R 5 NH][OOCH], preferably [Et 3 NH][OOCH], with or without formic acid.
• the [R 3 R 4 R 5 NH][OOCH] is added to the reaction mixture at the start of the process.
• Preferably less than two equivalents of [R 3 R 4 R 5 NH][OOCH] are used, preferably about one equivalent.
• Suitably less than 0.5 equivalents of formic acid are added to the reaction mixture at the start of the process, most preferably less than 0.2 equivalents. Further formic acid may be added to the reaction mixture during the course of the reaction.
• the hydride source is [M][OOCH] x , preferably NaOOCH, and formic acid.
• the [M][OOCH] x is added to the reaction mixture at the start of the process.
• Preferably less than two equivalents of [M][OOCH] x are used, preferably about one equivalent.
• Suitably less than 1.5 equivalents of formic acid are added to the reaction mixture at the start of the process, preferably less than 1 equivalent, most preferably less than 0.2 equivalents. If less than 1 equivalent of formic acid is added at the start of the process, further formic acid should be added during the course of the reaction, providing about 1-3 equivalents of formic acid in total.
• the process of the invention allows for reduced quantities of hydride source reagents than prior art methods, e.g. the process of WO 2004/03115 wherein pH is not controlled uses seven equivalents of formic acid and 2.7 equivalents of triethylamine. h ⁇ particular, the process of the present invention minimises the hazards associated with adding large quantities of formic acid to the reaction mixture at the start of the reaction.
• the pH of the reaction mixture is maintained between 6.5 and 8 during the course of the reaction. Control of pH is essential to provide good conversions and acceptably high product yields, preferably above 85%, whilst using acceptably low quantities of catalyst (e.g. a substrate: catalyst ratio of 500 or more).
• the pH can be monitored by methods known to those skilled in the art, but a preferred method is to use a Hamilton gel-filled electrode as described in the Examples of the present invention.
• the preferred method of controlling the pH is to add formic acid in a controlled manner during the course of the reaction, e.g. by titration. Most preferably, the pH is maintained from 7.0 to 7.8 by the controlled addition of formic acid.
• the hydride source is NR 3 R 4 R 5 and formic acid
• up to 1.5 equivalents of formic acid may be added at the start of the process and then further formic acid may be added as necessary to maintain the pH.
• the formic acid is added in a gradual, controlled manner because this minimises the hazards associated with decomposition of formic acid.
• the hydride source comprises [R 3 R 4 R 5 NH][OOCH]
• the formic acid is suitably added in a gradual, controlled manner, e.g. dropwise by titration, thus maintaining the pH from 6.5 to 8.
• the hydride source is [M][OOCH] x and formic acid
• up to 1.5 equivalents of formic acid may be added at the start of the process and then further formic acid may be added as necessary to maintain the pH.
• Suitable solvents may comprise dimethylformamide (DMF), ethyl acetate (EtOAc), acetonitrile, isopropyl acetate, tetrahydrofuran, 1,2-dichloroethane, dimethoxy ethane and/or water. It is preferred that the solvent comprises at least one polar aprotic solvent such as DMF or acetonitrile because these solvents are miscible with both organic and inorganic phases.
• standard non-deoxygenated reagent grade solvents are suitable for use in the process of the present invention.
• a preferred solvent system for the process of the present invention is a mixture of two or more solvents selected from DMF, EtOAc, acetonitrile and water.
• the solvent suitably comprises 0-25% DMF, 0-25% water and 75-95% EtOAc or 0-25% acetonitrile, 0-25% water and 75-95% EtOAc, preferably 0-20% DMF, 5-20% water and 80-90% EtOAc.
• the most preferred solvent is 10% DMF, 10% water and 80% EtOAc.
• the solvent suitably comprises 5-25% DMF and 75-95% EtOAc, 5-25% acetonitrile and 75- 95% EtOAc, 5-25% DMF and 75-95% water, or 5-25% acetonitrile and 75-95% water
• the solvent suitably comprises 0-25% DMF, 0-25% water and 75-95% EtOAc or 0-25% acetonitrile, 0-25% water and 75-95% EtOAc, preferably 0-20% DMF, 5-20% water and 80-90% EtOAc.
• phase transfer catalysts include quaternary alkyl ammonium halides, such as for example Bu 4 NBr.
• the ratio of phase transfer catalyst to catalyst is suitably from 0.01 to 0.5, preferably about 0.1.
• the reaction can be carried out at different temperatures and pressures. Suitably the reaction is carried out at atmospheric pressure and at the reflux temperature of the preferred solvent system. An external temperature of 100-120 0 C, more preferably 105- HO 0 C is appropriate for the most preferred solvent systems.
• reaction time will depend on key factors such as the ratio of oxcarbazepine to catalyst.
• the reaction should be completed in less than 36 hours, more preferably in less than 24 hours and high yields have been achieved by applying the process of the present invention in reaction times of less than 24 hours at oxcarbazepine to catalyst ratios even greater than 2000: 1.
• the product may spontaneously precipitate from the reaction mixture as it cools from reflux temperature.
• a suitable solvent preferably methyl tert-butyl ether (MTBE) is added to the reaction mixture before filtration.
• the product may be isolated by precipitating the crude product from suitable solvent mixtures, preferably either methanol/water or methanol/MTBE at 0-5 0 C.
• the work-up procedures are particularly simple compared to prior art methods such as those disclosed in WO 2004/031155 wherein the work-up procedure requires neutralisation of excess formic acid, extraction, drying, solvent evaporation and flash chromatography. These procedures are unsuitable for large-scale manufacture.
• the simple work-up procedures result in acceptably low residual ruthenium content in the isolated product, consistent with its intended use as a final intermediate in the manufacture of APIs,
• the (S)-(+)-10,l l-dihydro-10-hydroxy-5H- dibenz/b,f/azepine-5-carboxamide or (R)-(-)-10,l l-dihydro-10-hydroxy-5H- dibenz/b,f/azepine-5-carboxamide may be precipitated by removing the reaction solvent while adding water to maintain the reaction volume at a substantially constant level.
• the reaction solvent which is preferably ethyl acetate, may be removed by distillation.
• the distillation temperature is preferably at least 60°C.
• the weight of water replacing the reaction solvent may be in the range 80-120%, more preferably 90-1 10% of the weight of the solvent removed.
• the removal of the precipitated (S)-(+)- 10,11 -dihydro- 10-hydroxy-5H-dibenz/b,f/azepine-5-carboxamide or (R)-(-)- 10,l l-dihydro-10-hydroxy-5H-dibenz/b,f/azepine-5-carboxamide may subsequently be isolated by filtration, and can be further purified, preferably by reslurrying in a solvent, which is preferably ethyl acetate and re-filtration.
• Another advantage of the present invention is that it is possible to run the reaction with a high substrate concentration e.g. 0.5-1.5M, so that the volume efficiency of the reaction is very good. This is especially relevant when considering large-scale manufacturing.
• the (S)-(+)-10,l 1 -dihydro- 10-hydroxy-5H-dibenz/b,f/azepine-5-carboxamide or (R)-(-)- 10,11 -dihydro- 10-hydroxy-5H-dibenz/b,f/azepine-5-carboxamide produced according to the process of the present invention may be used as an API and formulated into finished pharmaceutical products, or may be converted by further chemical transformation to another API, e.g.
• (S)-(-)-10-acetoxy-10,l l-dihydro-5H- dibenz/b,f/azepine-5-carboxamide may be provided by esterif ⁇ cation of (S)-(+)-10,l l- dihydro-10-hydroxy-5H-dibenz/b,f/azepine-5-carboxamide.
• the present invention further provides a process for preparing a compound of formula (C) or (D)
• R 6 is hydrogen, alkyl, halogenalkyl, aralkyl, cycloalkyl, cycloalkyalkyl, alkoxy, aryl or pyridyl; comprising a first step, which is a process for the production of (S)-(+)- 10,1 l-dihydro-10-hydroxy-5H-dibenz/b,f/azepine-5-carboxamide or (R) ⁇ ( ⁇ )-10,l 1- dihydro-10-hydroxy-5H-dibenz/b,f/azepine-5-carboxamide according to the invention, and a second step, wherein the (S)-(+)- 10,11 -dihydro- 10-hydroxy-5H- dibenz/b,f/azepine-5-carboxamide or (R)-(-)-10,l 1 -dihydro- 10-hydroxy-5H- dibenz/b,f/azepine-5-carboxamide is acylated.
• R 6 may be straight or branched Ci -I8 alkyl, which may be substituted with halogen (F, Cl, Br or I). It may also be cycloalkyl (a cyclic C 3 -C 6 saturated group) or aiyl (unsubstituted phenyl or phenyl substituted by alkoxy, halogen or nitro group). Preferably R 6 is CH 3 .
• Compounds of formula (C) and (D) are further described in US 5,753,646. Suitable acylation methods are described in US 5,753,646 and WO 02/092572, e.g.
• (S)-(+)-10,l l-dihydro-10-hydroxy-5H-dibenz/b,f/azepine-5- carboxamide may be reacted with acetylchloride or acetic anhydride in dichloromethane to give (S)-(-)-10-acetoxy-10,l l-dihydro-5H-dibenz/b,f/azepine-5-carboxamide.
• Example 1 Asymmetric Reduction of Oxcarbazepine using NEfa and pH-controlled addition of HCOOH
• the catalyst formed separately in situ in a 5OmL Schlenk tube under N 2 flow by stirring [RuCl 2 ( ⁇ -cymene)] 2 (0.1588mmol, 97.2mg) and (S 1 S)-TsDAEN (2.2eq. with respect to the metal dimer precursor, 0.3493mmol, 159mg) in DMF (13mL, degassed, anhydrous) at room temperature for 10-15min. was injected.
• the Schlenk tube was rinsed with small portions of the remaining DMF (5x7mL) and injected to the reaction mixture.
• the solvent combination at this point was 10% DMF-10%H 2 O-80%EtO Ac (v/v/v) and the substrate concentration before titration was 1.1M.
• oxcarbazepine was charged (159mmol, 4Og), the flask fitted with a water reflux condenser connected to a Schlenk line, a burette for titration and a Hamilton gel filled electrode fitted through a hollow GL25 screw cap with a PTFE/silicone ring.
• the flask was flushed with N 2 for approximately 30min.
• EtOAc 80mL, degassed, anhydrous
• [Et 3 NH][OOCH] commercially available from Fluka (1.07 eq., 170mmol, 25mL, undegassed, Fluka
• the catalyst formed separately in situ in a 2OmL Schlenk tube by stirring [RuCl 2 (p ⁇ cymene)] 2 (0.0265mmol, 16.2mg) and (S 1 S)- TsDAEN (2.2 eq. with respect to the metal dimer precursor, 0.0582mmol, 25mg) in DMF (5mL, degassed, anhydrous) at room temperature for 10-15min. was injected.
• DMF 5mL, degassed, anhydrous
• the Schlenk tube was rinsed with small portions of the remaining DMF (5x3mL) and injected to the reaction mixture.
• the solvent combination at this point was 20%DMF- 80%EtOAc (v/v) and the oxcarbazepine concentration before titration was 1.3M.
• Comparison Ia Asymmetric reduction with and without pH Control (Hydride source is NEb and HCOOH)
• Reactions were carried out using a method similar to that of example 1.
• the substrate/catalyst ratio was 2000 and the solvent was 20% H 2 0/Et0Ac.
• the ligand was (S 5 S)-Ts-DAEN.
• leq. NEt 3 and leq. HCOOH were added to the reaction mixture at the start of the reaction. Further HCOOH was added throughout the course of the reaction to maintain a pH of 7.4.
• 4.4eq. Et 3 N and 4eq. HCOOH were pre-mixed in H 2 O and added to the reaction mixture in EtOAc at the beginning of the reaction. Table 1 shows the results of example 3 and comparative example 1:
• Comparison Ib Asymmetric reduction with and without pH Control (Hydride source is fEkNHHOOCHl or fEt ⁇ NHHOOCHl and HCOOH)
• a comparison of comparative examples 4 and 5 with example 4 shows that by controlling the pH by addition of HCOOH, a much smaller quantity of the expensive reagent [Et 3 NH][OOCH] can be used, and the reaction reaches almost complete conversion in 7 hours rather than 20-25 hours.
• catalysts comprising the (S,S)-TsDAEN and (S,S)-TsDPEN ligands was compared at a 20-4Og scale.
• the catalysts were generated in situ by stirring [RuCl 2 (p-cymene)] 2 and either (S 5 S)-TsDAEN or(S,S)-TsDPEN for 5-10 minutes in DMF before addition to oxcarbazepine and 1.07 equivalents of [Et 3 NH][OOCH].
• the ratio of oxcarbazepine to catalyst was 3000:1.
• Table 4 shows the results for Examples 5 and 6 (using (S 5 S)-TsDAEN) and example 7 (using (S 5 S)-TsDPEN): Table 4
• the (S 5 S)-TsDAEN examples show significantly better conversion than the (S 5 S)- TsDPEN example and show similar enantioselectivity.
• Table 5 shows the results of three asymmetric reduction reactions wherein a phase transfer catalyst was used in addition to the ruthenium catalyst.
• the catalyst was generated in situ by adding [RuCl 2 ( ⁇ -cymene)] 2 and a ligand to EtOAc and stirring.
• (NB (R 5 R)-TsDTEN has the same structure as (R 5 R)-TsDPEN except that the phenyl groups are substituted by tolyl groups).
• the phase transfer catalyst was 0.1 equivalents Of Bu 4 NBr.
• the hydride source was 2 equivalents of [Et 3 NH][OOCH] and additional formic acid was slowly added to the reaction mixture during the course of the reaction.
• the ratio of oxcarbazepine to catalyst was 2000:1 and the external reaction temperature was HO 0 C.
• the conversion in example 9, wherein the ligand was (R,R)- TsDAEN was significantly better than the conversion in examples 8 and 10, wherein the ligands were (S 5 S)-TsDPEN and (R,R)-DTEN.
• the reaction mixture was then quenched by the addition of sulphuric acid. After stirring for 10 min, the layers were separated. The organic layer was washed twice with saturated aqueous sodium bicarbonate solution and then water. Approximately half of the dichloromethane was then removed by evaporation and isopropanol (5 L) was added to the mixture which was then left to stand overnight. Further solvent was evaporated (approximately 1.5L) and the resulting slurry was cooled to approximately 3 0 C. After 3 hours the solid was filtered off, washed with cold isopropanol and then dried iinder vacuum overnight. The dried solid was suspended in isopropanol (6.5 L) and the resulting white slurry was heated to reflux.
• Residual ruthenium content was found to be less than 2ppm. According to the regulatory guidelines, the oral concentration limit is 5ppm.
• Example 4 Asymmetric reduction of Oxcarbazepine using higher oxcarbazepine: catalyst ratio
• Ethyl acetate was distilled from the batch while maintaining the original batch volume by the addition of water (dropwise). Temperature was maintained above 60 0 C during the distillation. Approximately 1/3 into the distillation the product started to precipitate.

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